1. Field
This invention relates to electrosurgical apparatus and methods, such as those typified by devices marketed under the trademark "BOVIE.RTM." by MDT Corporation of Torrance, Calif. It is particularly directed to an improved method for determining the amount of energy dispensed during electrosurgical procedures into a patient.
2. State of the Art
Electrosurgical procedures, as generally practiced, involve the placement of a patient upon a large surface area electrode, commonly referred to as a dispersive plate. The plate electrode constitutes a first electrode associated with an electrosurgical generator. An electrosurgical instrument, which constitutes a second electrode associated with the electrosurgical generator is utilized to perform surgical procedures on the anatomy of a patient. As the instrument makes contact with the patient's body, energy is dispensed into the patient by virtue of the electrical circuit comprised of the dispersive plate electrode, the patient, the surgical instrument, and the electrosurgical generator. The rate at which energy is dispensed into the patient is conventionally defined as power.
Common electrosurgical procedures involve the cutting, abrading, vaporizing or cauterizing of the patient's tissues. As a consequence, significant amounts of energy are dispensed to the patient's body. For reasons of patient safety, and consistent with conservative surgical procedures generally, it is desirable for a surgical team to be able to estimate with reasonable accuracy the amount of electrical energy dispensed into a patient over discrete intervals of time involved in the surgical procedures. It is particularly important for the surgical team to monitor the total energy dispensed into the patient's body during the entire procedure from start to finish. Unfortunately, available electrosurgical devices provide no reliable basis from which accurate determinations of energy dispensed into a patient can be derived.
The control panels of electrosurgical generators typically include a power setting which indicates a percentage of maximum operating power. That is, the generator may be set at 100 percent, 50 percent, or some other selected value. That setting value is not precisely indicative of the actual rate (e.g., watts) at which power is delivered to the patient, however, because that value is dependent upon factors which affect the actual power deliverable at any time by the generator. Most notable among these is the highly variable impedance value contributed by the patient to the circuit. The power output of an electrosurgical generator is a function of load impedance, including the dominant contribution of the patient. Patient impedance varies considerably during a procedure as well as from patient to patient. Although certain available electrosurgical generators display a power value which reflects increased or decreased current flow, the power value displayed is computed from periodic current measurements made into a known, fixed impedance. The fixed impedance value does not correspond to the actual impedance in the circuit. Accordingly, the power value displayed may actually be misleading to the surgical team. To the extent the power value for a given procedure is made a matter of record, it is largely valueless and non-reproducible. Without accurate real time measurements of power (watts), it is not possible to obtain an accurate integrated quantity (e.g. watt hours) reflective of the total energy dispensed to a patient during an elapsed time.
For meaningful record keeping, and assistance in the repeatability of a procedure, for patient's safety, and for purposes of meaningful research involving patient energy tolerances or related matters, there remains a need for a method whereby the quantity of energy dispensed to a patient or research target in an electrosurgical procedure may be reliably measured.